Nucleation and morphology of sodium molybdate dihydrate from NaOH solution

The induction time for sodium molybdate dihydrate crystallization from NaOH solution at 40 °C and 60 °C was investigated by experiment and the primary nucleation was also identified according to the classical nucleation theory. The bipyramidal truncated crystals and the nearly rectangular parallelepiped crystals were obtained at high supersaturation and low supersaturation, respectively. The interfacial free energy, surface entropy factor, critical nucleation free energy, critical nucleus size and critical nucleation molecular number of bipyramidal truncated crystals were conducted. The nearly rectangular parallelepiped crystals are considered more stable than the bipyramidal truncated crystals, and high supersaturation and high temperature are more conducive to nucleation of sodium molybdate dihydrate crystals. Finally, the normal growth mechanism for Na2MoO4·2H2O crystallization was identified with various models and the surface entropy factor.